Sandwich diaphragm for mill

ABSTRACT

A diaphragm in the form of a composite sieving device for use in a rotary grinding mill containing loose grinding bodies for grinding solid materials is disclosed. The device comprises a sandwich structure which includes a plurality of plate-like members in intimate contact with one another. The plate-like members acting in combination prevent the passage of the grinding bodies and oversized particles of the material being ground from one section of the mill to another.

United States Patent 11 1 Hansen et al.

[ Dec. 4, 1973 SANDWICH DIAPHRAGM FOR MILL [75] Inventors: Claus M. Hansen; Ejvind N.

Norgaard, both of Copenhagen-Volby, Denmark [73] Assignee: F. L. Smidth & Co., Cresskill, NJ.

[22] Filed: Jan. 5, 1972 [21] Appl. No.: 215,475

[30] Foreign Application Priority Data Jan. 15, 1971 Great Britain 2,123/71 521 U.S. c1 241/72, 241/78, 241/153 51 1m, 01, B020 17/02 Gfi iim or's'arii ..'..241/70'-72, 73, 74, 76, 78, 241/79.2,79.3,ss,2s4, 181,153

[56] References Cited UNITED STATES PATENTS 1,361,205 12/1920 Van Zandt 241/72 X 1,793,495 2/1931 Lee et a] 241/70 3,599,882 8/1971 Sabaski et 241/70 FOREIGN PATENTS OR APPLICATIONS 13,852 7/1905 Great Britain 241/70 Primary Examiner-Granville Y. Custer, Jr. Assistant Examiner-Howard N. Goldberg Attorney-Dean S. Edmonds et al.

[57] ABSTRACT A diaphragm in the form of a composite sieving device for use in a rotary grinding mill containing loose grinding bodies for grinding solid materials is disclosed. The device comprises a sandwich structure which includes a plurality of plate-like members in intimate contact with one another. The plate-like members acting in combination prevent the passage of the grinding b0- dies and oversized particles of the material being ground from one section of the mill to another.

12 Claims, 5 Drawing Figures I PATENTEUUEB 4m 1 3,776'477 FIG. 1-

PATENTEDUEB 41m SHEET 2 BF 4 FIG. 3

PATENTED 4 SHEET u BF 1 FlG.. 5'

SANDWICH DIAPHRAGM FOR MILL BACKGROUND OF THE DISCLOSURE The invention relates to grinding tube mills of the kind charged with loose grinding bodies, and in particular, to a composite sieving device used in the grinding mills. These grinding mills are generally used as continuously operating grinding machines for grinding solid materials in numerous industries, including the cement industry, inter alia for grinding cement raw materials so as to obtain cement raw meal, or cement raw slurry, or for grinding cement clinker together with a small amount of gypsum with a view to obtain cement, such as Portland cement.

Mills of this kind generally comprise a hollow cylin drical mill body equipped at each end with a hollow trunnion resting in a bearing so as to enable the mill to be rotated about a horizontal axis by a prime mover. Material to be ground is continuously fed to the rotating mill through one of its hollow trunnions, the inlet trunnion, and ground material is discharged through the other outlet trunnion. The interior of the mill has one, two, three or four compartments for containing grinding bodies in use. In a mill with only one compartment, an outlet end wall of the compartment is in the form of a diaphragm designed to allow sufficiently ground material, but not the grinding bodies, to pass to the outlet trunnion. More commonly, the interior of a mill of this kind is divided by one, two or three such diaphragms into two, three or four compartments. Each compartment has a charge of grinding bodies the size of which decreases from compartment to compartment in the direction of conveyance of the material that is being ground. The material to be ground is fed through the inlet trunnion to the first compartment containing the largest grinding bodies. On being conveyed through this compartment, the particles of the material are reduced in size, and at length they pass through the diaphragm between the first and second compartments. The diaphragm has openings through which the material being ground can pass. The openings in the diaphragm are small enough to prevent the grinding bodies in the first compartment passing through to the next compartment. What has just been described is repeated in the successive compartments and the finished, ground material'leaves the last compartment of the mill which contains the smallest grinding bodies, and is discharged from the mill through the outlet trunnion. The material preferably passes a final, outlet diaphragm between the last compartment and the outlet trunnion.

The mills used in the cement industry today ordinarily have three compartments and consequently two intermediate diaphragms and an outlet diaphragm adjacent to the mill end wall. The charge of grinding bodies in the first compartment comprises balls varying in diameter between, say, 100 and 50 mm, and in the second compartment the balls may vary between 60 and 30 mm. The third compartment usually has a charge of cylindrical grinding bodies of a diameter and length varying between, say 25 and mm, the diameter usually being equal to the length. The grinding bodies are subject to wear during the grinding operating and must be renewed from time to time.

The mill is normally fed with materials having a maximum overall size of, say, 30 mm and is ground in the mill to cement fineness.

The primary purpose of the diaphragm is to prevent the grinding bodies from passing from one compartment into the next or from the last compartment out of the mill, but the openings in the diaphragm are made smaller than what would just serve to satisfy this purpose. This is done in order, as far as possible, to prevent any passage of particles of material into the next compartment unless they have been ground down to the particle size range prescribed for that compartment, i.e., the particle size range giving optimum grinding conditions in the compartment in question.

With the design presently being used for diaphragms, it is not even approximately possible to ensure that only particles of the desired size pass through. This is due to the fact that to possess the rigidity, sturdiness and wear resistance required to withstand the blows from the grinding bodies and the pressure exerted on the diaphragm by them, the diaphragm must have a minimum thickness. On the other hand, in a diaphragm through which only sufficiently ground material will pass, the openings must be less than a given size. Unfortunately, these two requirements are not compatible except by providing narrow openings in a thick plate. Such openings are not readily penetrable by the material, and are quickly clogged by the material. This tendency is increased by the fact that nibs become wedged in the mouths of the openings.

The openings must therefore be made considerably larger than the theoretical maximum size with the consequence that, for instance, in the third grinding compartment of the mill a considerable number of particles, so-called oversize grains, will be found that should have remained longer in the second compartment so as to be further reduced in size.

It is the object of the present invention to overcome the difficulties referred to hereinabove.

SUMMARY OF THE INVENTION According to the invention the diaphragm, or at least one of the diaphragms, of a mill of the kind referred to is in the form of a composite sieving device comprising two members in intimate contact with each other, of which, the first, thicker member faces the inlet of the mill and has openings whose size is such as to allow the passage of the material to be ground, but not the grinding boeies, and the second, thinner member faces the mill outlet and has openings which are smaller than those in the first member and prevent oversize grains from passing through the diaphragm.

As will be seen, the prevention of the passage of grinding bodies and oversize grains through the diaphragm is now achieved by two members of a sieving device acting in combination. The second member, which may be a thin plate or the like, has openings which, though small enough to block oversize grains, are large in relation to the members thickness and which therefore allow only sufficiently ground material to pass without any clogging occurring. The first member, whose openings need only be just small enough to prevent the grinding bodies from passing, may be as thick and strong as may be necessary to withstand the mechanical stresses produced by the change and so protects the second member with which it is in intimate contact. The openings in the first member which may also be of plate form, can therefore be larger than in a conventional diaphragm, with the result that they will not be clogged either.

The diaphragm is of course subjected to wear, but it is found that the wear on the thick, first member is tolerable just because of its thickness, whereas the wear on the thin second member is negligible.

It is also found that there may be practically no clogging and no passage of oversize grains, and that in many cases in a three-compartment mill the first diaphragm may be dispensed with when the ordinary second diaphragm is replaced by one including a sieving device according to the invention. In other words, the mill can be transformed into a two-compartment mill and the installation and upkeep of one diaphragm is saved, which is very important; moreover the mill works better.

The two members may be supplemented by a third member which is of sturdy construction and is in intimate contact with the outlet-facing side of the second member and which has openings in register with those of the first member and of a size not less than these. This third member serves to strengthen the construction further and to prevent the pressure of the charge of grinding bodies and material to be ground forcing the second member out of intimate contact with the first.

Advantageously, the third member is an exact copy of the first member at least with regard to the number, size, form and distribution of its openings.

The first member may be equipped with ribs extending substantially radially at that side of the member which faces the inlet of the mill. During the rotation of the mill these ribs produce a space which is substantially free from whole and broken grinding bodies and other foreign bodies such as pieces of iron bolts and chains that might be pressed into the openings of the first member. In addition, the ribs serve to increase the rigidity and stiffness of the first member.

The second member is preferably a plate of a thickness from 3 to 6 mm, the openings preferably being slots, advantageously from 2 to 5 mm, and best from 3 to 4 mm wide.

Alternatively, the second member may be a grate composed of crossing or plated bars or wires. Such a member will invariably be thicker than a plate, but its total opening area may be made substantially greater, say, 55 to 60 percent, as against about 40 percent for a suitably perforated plate.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross section through a diaphragm in a mill in accordance with the invention;

FIG. 2 is a cross section on a larger scale through another mill;

FIG. 3 is a front view of the diaphragm taken along line 3-3 of FIG. 2;

FIG. 4 is a section taken along line 44 of FIG. 2; and,

FIG. 5 is a section taken along line 5-5 of FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a mill rotating about an axis 1, the mill body proper 2 having a lining 3. A single diaphragm is provided and is constituted by a sieving device composed of a first member 4 and a second member 5 bolted together by means of bolts not shown. Rings 6 and 7 keep these members in position. The members have central openings 8 and 9, respectively. The charge (not shown), consisting of grinding bodies and material to be ground, does not rise above the lower edges of these openings.

The diaphragm shown in FIG. 1 separates the second and the third grinding compartments of the mill, the former being to the left and the latter to the right of the diaphragm. Thus, the material to be ground moves continuously from left to right at the desired speed if and when the particles are fine enough to pass through the perforations of the member 5 and if the uncovered total area of the openings is correlated to the desired speed of conveyance, i.e., to the capacity of the mill.

The two members 4 and 5 of FIG. 1 can advantageously be supplemented by a third member in the space now occupied by the ring 7. This member should be identical in every respect to the member 4.

In contrast to FIG. 1, FIGS. 2 to 5 show a double diaphragm, of which the sieving device according to the invention forms part. In these figures a ring 10, corresponding to the rings 6 and 7 in FIG. 1, is fastened to the mill shell body by means of bolts 11. This ring has a number of projections 12 against which a solid plate 13 having a central opening is pressed by means of fixing bolts 14. To the side of this plate, facing the mill outlet, wear-resistant lining plates 15 are fastened by means of bolts 16. At some distance from and parallel to the plate 13 at the side thereof opposite to the lining plates 15 is a third member 17, which is fastened to and spaced away from the plate 13 by staybolts 18. The plate 17 is shown in FIG. 5 and it will be seen that the openings in it are so large that the plate might more appropriately be termed a skeleton or framework.

The second member, which is best seen in FIG. 4, and which takes the form of several sector-shaped plates 19 having perforations 28 all over, is secured to this framework by screws 27.

The so-called first member (or coarse grate) is shown more clearly in FIG. 3 at 20. This member is composed of several sector-shaped units, each having slots 22 and being pressed tightly against the perforated plate units by means of bolts 21 which pass through the whole diaphragm, including the wear plates 15. As presently preferred, slots 22 are advantageously about 10 to 50 mm. in width.

As will be seen, this diaphragm constitutes a very rigid construction. The space available between the plates 17 and 13 may be used for various purposes, particularly to receive suitable lifting devices to enable the material which has passed through the sieving device to pass out through the central opening of the plate 15 and into the next mill compartment.

The members 20, 19 and 17 have a common central circular opening 23, into which a ring-shaped member 24 of curved cross-section is inserted. The central opening of this ring receives a circular solid plate 25 having openings 26. The members 24 and 25 serve to prevent any stray grinding ball or any unexpected spurt of material originating from the compartment to the left from finding its way through the opening 23 into the compartment to the right. These parts of the double diaphragm are not subjected to any mechanical stress worth mentioning and are therefore of lighter construction.

Ribs 29 are provided as shown. During the rotation of the mill these ribs produce a space which is substantially free from whole and broken grinding bodies and other foreign bodies such as pieces of iron bolts and chains. If the member is a casting, the ribs may be cast integrally with it or they may be welded or bolted to it. If the member 20 is fabricated by welding, the ribs may be welded or bolted to it as may be convenient.

Of course, there need only be perforations in the plate 19 in the areas corresponding to the slots 22 in the plate 20, but the provision of a plate having perforations all over permits the use of commercially available standard plates provided with circular, square or oblong openings.

We claim:

1. A grinding tube mill for grinding solid materials comprising a hollow cylindrical body including inlet means for receiving the material to be ground and outlet means for removing the ground material; a plurality of loose grinding bodies for crushing the solid material; and at least one diaphragm in the form of a composite sieving device, said device comprising a first and second member, said first member facing the inlet of the mill and being thicker then the second member, said first member including a plurality of openings of a size which allows the material being ground in the mill to pass therethrough, but not the grinding bodies; a second member being sandwiched between the first and a third member and including a plurality of openings smaller than those of the first member and which substantially prevents oversized ground material from passing therethrough, and a third member in contact with the second member and having a plurality of openings in register with and of a size at least equal to the openings of the first member, the members being in intimate contact with each other.

2. A grinding mill according to claim 1 wherein the third member is an exact copy of the first member with regard to the number, size, form and distribution of its openings.

3. A grinding mill according to claim 1 wherein the first member is provided with ribs extending substantially radially at that side of the member which faces the inlet of the mill.

4. A grinding mill according to claim 1 wherein the second member is a plate having a thickness of about 3 to 6mm.

5. A grinding mill according to claim 4 wherein the openings in the second plate-like member are slots.

6. A grinding mill according to claim 5 wherein the width of the slots in the second member is between about 2 to 5mm.

7. A grinding mill according to claim 6 wherein the width of the slots in the second member is between about 3 to 4mm.

8. A grinding mill according to claim 1 wherein the second member is a grate composed of crossing or plaited bars or wires.

9. A grinding mill according to claim 1 wherein the openings in the first member are slots.

10. A grinding mill according to claim 9 wherein the width of the slots in the first member is between about 10 to 50mm.

11. A grinding mill according to claim 1 wherein the mill includes from two to four of said diaphragms.

12. A diaphragm in the form of a composite sieving device for use in a grinding mill charged with loose grinding bodies comprising a first and second member, said first member being thicker than the second member and including a plurality of openings of a size which allows the material being ground in the mill to pass therethrough, but not the grinding bodies; a second member being sandwiched between the first and a third member and including a plurality of openings smaller than those of the first member and which substantially prevents oversized ground material from passing therethrough; and a third member in contact with the second member and having a plurality of openings in register with and of a size at least equal to the opening of the first member, the members being in intimate contact with each other. 

1. A grinding tube mill for grinding solid materials comprising a hollow cylindrical body including inlet means for receiving the material to be ground and outlet means for removing the ground material; a plurality of loose grinding bodies for crushing the solid material; and at least one diaphragm in the form of a composite sieving device, said device comprising a first and second member, said first member facing the inlet of the mill and being thicker then the second member, said first member including a plurality of openings of a size which allows the material being ground in the mill to pass therethrough, but not the grinding bodies; a second member being sandwiched between the first and a third member and including a plurality of openings smaller than those of the first member and which substantially prevents oversized ground material from passing therethrough, and a third member in contact with the second member and having a plurality of openings in register with and of a size at least equal to the openings of the first member, the members being in intimate contact with each other.
 2. A grinding mill according to claim 1 wherein the third member is an exact copy of the first member with regard to the number, size, form and distribution of its openings.
 3. A grinding mill according to claim 1 wherein the first member is provided with ribs extending substantially radially at that side of the member which faces the inlet of the mill.
 4. A grinding mill according to claim 1 wherein the second member is a plate having a thickness of about 3 to 6mm.
 5. A grinding mill according to claim 4 wherein the openings in the second plate-like member are slots.
 6. A grinding mill according to claim 5 wherein the width of the slots in the second member is between about 2 to 5mm.
 7. A grinding mill according to claim 6 wherein the width of the slots in the second member is between about 3 to 4mm.
 8. A grinding mill according to claim 1 wherein the second member is a grate composed of crossing or plaited bars or wires.
 9. A grinding mill according to claim 1 wherein the openings in the first member are slots.
 10. A grinding mill according to claim 9 wherein the width of the slots in the first member is between about 10 to 50mm.
 11. A grinding mill according to claim 1 wherein the mill includes from two to four of said diaphragms.
 12. A diaphragm in the form of a composite sieving device for use in a grinding mill charged with loose grinding bodies comprising a first and second member, said first member being thicker than the second member and including a plurality of openings of a size which allows the material being ground in the mill to pass therethrough, but not the grinding bodies; a second member being sandwiched between the first and a third member and including a plurality of openings smaller than those of the first member and which substantially prevents oversized ground material from passing therethrough; and a third member in contact with the second member and having a plurality of openings in register with and of a size at least equal to the opening of the first member, the members being in intimate contact with each other. 